Electrophotography is a useful process for printing images on a receiver (or “imaging substrate”), such as a piece or sheet of paper or another planar medium (e.g., glass, fabric, metal, or other objects) as will be described below. In this process, an electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (i.e., a “latent image”).
After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor and are attracted to the latent image to develop the latent image into a toner image. Note that the toner image may not be visible to the naked eye depending on the composition of the toner particles (e.g., clear toner).
After the latent image is developed into a toner image on the photoreceptor, a suitable receiver is brought into juxtaposition with the toner image. A suitable electric field is applied to transfer the toner particles of the toner image to the receiver to form the desired print image on the receiver. The imaging process is typically repeated many times with reusable photoreceptors.
The receiver is then removed from its operative association with the photoreceptor and subjected to heat or pressure to permanently fix (i.e., “fuse”) the print image to the receiver. Plural print images (e.g., separation images of different colors) can be overlaid on the receiver before fusing to form a multicolor print image on the receiver.
In a common type of printing system, the electrostatic latent image is formed by exposing the photoreceptor with a linear printhead including a linear array of light sources (e.g., LEDs). The printhead generally includes an array of lenslets which focus the light from the light sources onto the surface of the photoreceptor. The lenslets typically have a narrow depth of focus, which requires that the focus position of the printhead be adjusted to be within a very tight tolerance. Typically, a manual focus adjustment is performed in a specially designed fixture during the assembly of the linear printhead. However, this focusing adjustment does not account for variability in the mounting system for the linear printhead in the printing system. As a result, the focus position of the printhead may not be within acceptable tolerances. Because of the small spacing between the printhead and the photoreceptor, it is not practical to directly access the focus characteristics of the linear printhead after it has been installed the printing system. There remains a need for a simple and efficient method for accurately adjusting the focus position of the printhead after it has been mounted in the printing system.